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Responsiveness and adaptability of xylogenesis dynamics in Eucalyptus cladocalyx
Thesis (PhD)--Stellenbosch University, 2025.
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| Language: | English |
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867614027945869312 |
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| access_status_str | Open Access |
| author | Gama, Gugu Mbali |
| author2 | Drew, Dave |
| author_browse | Drew, Dave Gama, Gugu Mbali |
| author_facet | Drew, Dave Gama, Gugu Mbali |
| author_sort | Gama, Gugu Mbali |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134619 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:45:31.220Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/134619 Responsiveness and adaptability of xylogenesis dynamics in Eucalyptus cladocalyx Gama, Gugu Mbali Drew, Dave Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science. Eucalyptus -- Ecology Forest ecology Plant cells and tissues -- Physiology Xylem Thesis (PhD)--Stellenbosch University, 2025. Gama, G. M. 2025. Responsiveness and adaptability of xylogenesis dynamics in Eucalyptus cladocalyx. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/bba8c835-fcae-44c4-a7bf-5632284d5a76 ENGLISH ABSTRACT: Given the increasing variability of environmental conditions, many tree species—including Eucalyptus—face heightened vulnerability to climatic and developmental stressors. These changes directly affect xylem formation and biomass production, even in regions typically favourable for forest growth. Anatomical changes in xylem influence water transport efficiency, radial growth, and tree ring patterns, providing valuable clues for predicting species responses to environmental change. While most research has focused on commercially important species like E. grandis and E. globulus, drought-tolerant species such as E. cladocalyx remain understudied. This limits our understanding of how this species copes with water stress and how its wood properties adapt. Furthermore, factors such as inconsistent sampling, the selective focus of specific cell types, and a lack of standardized protocols, make comparisons across studies difficult. In response to these gaps, this study examined tree growth and xylem anatomy from pith to bark to better understand how young eucalypts of E. cladocalyx respond to water availability changes. The focus was on fine-scale changes in vessel and fiber traits, aiming to link anatomical variation to water transport, growth, and survival. A central component of the project involved developing a workflow that integrated robust histology techniques with image advanced imaging software capable of concurrently classifying xylem cell types, automating cell identification, and linking anatomical traits with environmental factors over time. This process provided parameters for growth and wood formation models under varying water-limiting conditions, and this process was also applied to E. grandis for a comparative analysis. In E. cladocalyx, vessel and fiber traits showed daily variation during cyclic drought, reflecting interactions between treatment and time. However, no significant differences in vessel area, frequency, fiber area, fiber thickness, or cambial cell counts were found between treatments. This suggests that anatomical traits may require more intense or prolonged drought to show clear changes. The stability of xylem structure and cambial activity under stress reflects the drought tolerance of E. cladocalyx and its ability to maintain hydraulic function despite reduced growth. Pre-drought conditioning further supported this resilience by helping optimize hydraulic safety and mechanical stability. In contrast, E. grandis displayed greater drought sensitivity. Under severe drought, non-preconditioned individuals showed significant reductions in vessel size, fiber wall thickness, and cambial activity. However, preconditioning mitigated these effects, preserving cambial function and moderating anatomical changes. This demonstrates the capacity of plasticity of E. grandis and the gradual adaptation when drought conditions develop progressively. The two species thus revealed contrasting drought-adaptive strategies: E. cladocalyx relies on structural conservatism to maintain xylem function, while E. grandis prioritizes rapid growth under favourable conditions but depends on anatomical plasticity to cope with water stress. Overall, these findings highlight the importance of integrating anatomical studies, advanced image analysis, and species-level comparisons to improve our understanding of eucalypt drought responses. However, challenges remain in characterizing diverse xylem cell types and linking anatomy to environmental data. There is a need for improved, open-access image tools that can automate cell classification, handle oblique cell arrangements, and accommodate diverse hardwood anatomies. Such advances are essential for linking wood traits to environmental conditions, especially as climate variability intensifies. AFRIKAANSE OPSOMMING: Gegewe die toenemende wisselvalligheid van omgewingstoestande, word baie boomspesies — insluitend Eucalyptus — al hoe meer vatbaar vir klimaats- en ontwikkelingsverwante stresfaktore. Hierdie veranderinge het 'n direkte invloed op xileemvorming en biomassa-produksie, selfs in streke wat tradisioneel as gunstig vir bosgroei beskou word. Veranderinge in xileemanatomie beïnvloed die doeltreffendheid van watervervoer, radiale groei, en boomring-patrone, en bied waardevolle insigte in spesie-spesifieke reaksies op omgewingsverandering. Terwyl navorsing hoofsaaklik gefokus het op kommersieel waardevolle spesies soos Eucalyptus grandis en E. globulus, is droogtebestande spesies soos E. cladocalyx steeds onderverteenwoordig in wetenskaplike studies. Hierdie leemte belemmer ons begrip van hoe hierdie spesie waterstres hanteer en hoe die hout eienskappe onder veranderende klimaattoestande aanpas. Daarbenewens bemoeilik faktore soos inkonsekwente monsternemingsmetodes, ’n beperkte fokus op spesifieke selsoorte, en die afwesigheid van gestandaardiseerde protokolle vergelykings tussen studies en beperk breër ekologiese en fisiologiese interpretasies. As reaksie op hierdie kennistekorte het die studie boomgroei en xileemanatomie van die merg tot by die bas ondersoek om 'n beter begrip te verkry van hoe jong E. cladocalyx individue reageer op veranderings in waterbeskikbaarheid. Die fokus was op fynskaalse veranderinge in vaarten vesel-eienskappe, met die doel om anatomiese variasie te koppel aan watervervoer, groei en oorlewing. ’n Sleutelelement van die projek was die ontwikkeling van ’n werkvloei wat robuuste histologietegnieke geïntegreer het met gevorderde beeldverwerkingsagteware wat in staat is om xileemseltipes gelyktydig te klassifiseer, selidentifikasie te outomatiseer, en anatomiese eienskappe oor tyd aan omgewingsfaktore te koppel. Hierdie proses het parameters verskaf vir groeimodelle en houtvormingsmodelle onder verskillende waterbeperkingsomstandighede, en is ook toegepas op E. grandis vir ’n vergelykende analise. In teenstelling hiermee het E. grandis groter droogtegevoeligheid getoon. Onder ernstige droogtetoestande het individue wat nie vooraf aan droogte blootgestel is nie, beduidende afnames in vaargrootte, veselwanddikte en kambiumaktiwiteit getoon. Voorafblootstelling (prekondisionering) het egter hierdie effekte versag, met behoud van kambiumfunksie en gematigde anatomiese veranderinge. Dit demonstreer die plastisiteitsvermoë van E. grandis en die geleidelike aanpassing wanneer droogtetoestande progressief ontwikkel. Die twee spesies het dus teenstellende droogteaanpassingsstrategieë onthul: E. cladocalyx steun op strukturele konserwatisme om xileemfunksie te handhaaf, terwyl E. grandis vinnige groei onder gunstige toestande prioritiseer, maar op anatomiese plastisiteit staatmaak om waterstres te hanteer. Algeheel beklemtoon hierdie bevindings die belangrikheid daarvan om anatomiese studies, gevorderde beeldontleding en spesie-vlakvergelykings te integreer om ons begrip van Eucalyptus-reaksies op droogte te verbeter. Tog bestaan daar steeds uitdagings in die karakterisering van die uiteenlopende xileemseltipes en die koppeling van anatomie aan omgewingsdata. Daar is ’n behoefte aan verbeterde, ooptoeganklike beeldanalise-instrumente wat selklassifikasie kan outomatiseer, skuins selrangskikkings kan hanteer, en die anatomiese diversiteit van hardehoutspesies kan akkommodeer. Sulke vooruitgang is van kardinale belang om houteienskappe aan omgewingstoestande te koppel—veral namate klimaatswisselvalligheid toeneem. Doctoral 2025-12-19T05:55:17Z 2025-12-19T05:55:17Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134619 en Stellenbosch University xi, 111 pages : illustrations. application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Eucalyptus -- Ecology Forest ecology Plant cells and tissues -- Physiology Xylem Gama, Gugu Mbali Responsiveness and adaptability of xylogenesis dynamics in Eucalyptus cladocalyx |
| title | Responsiveness and adaptability of xylogenesis dynamics in Eucalyptus cladocalyx |
| title_full | Responsiveness and adaptability of xylogenesis dynamics in Eucalyptus cladocalyx |
| title_fullStr | Responsiveness and adaptability of xylogenesis dynamics in Eucalyptus cladocalyx |
| title_full_unstemmed | Responsiveness and adaptability of xylogenesis dynamics in Eucalyptus cladocalyx |
| title_short | Responsiveness and adaptability of xylogenesis dynamics in Eucalyptus cladocalyx |
| title_sort | responsiveness and adaptability of xylogenesis dynamics in eucalyptus cladocalyx |
| topic | Eucalyptus -- Ecology Forest ecology Plant cells and tissues -- Physiology Xylem |
| url | https://scholar.sun.ac.za/handle/10019.1/134619 |
| work_keys_str_mv | AT gamagugumbali responsivenessandadaptabilityofxylogenesisdynamicsineucalyptuscladocalyx |